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Abstract
Developing chloroplasts were isolated from greening Cucumis cotyledons in a cofactor-enriched medium and were incubated in the dark with 14C-labeled and unlabeled magnesium-protoporphyrin monoester. The metabolic pools between protoporphyrin and protochlorophyllide were monitored spectrofluorometrically. The incorporation of the 14C label into protochlorophyllide was also determined. It was shown that magnesium-protoporphyrin monoester, a postulated intermediate of the chlorphyll biosynthetic pathway, was convertible into protochlorophyllide with relatively high yields. Since protochlorophyllide is the immediate precursor of chlorophyll a it was concluded that magnesium-protoporphyrin monoester was indeed an intermediate of the chlorophyll biosynthetic pathway.
Highlights
Developing chloroplasts were isolated from greening Cucumis cotyledons in a cofactor-enriched medium and were incubated in the dark with W-labeled and unlabeled magnesium-protoporphyrin monoester
Since protochlorophyllide is the immediate precursor of chlorophyll a it was concluded that magnesiumprotoporphyrin monoester was an intermediate of the chlorophyll biosynthetic pathway
Metalloporphyrins in Isolated Plastids - It was previously demonstrated (11) that developing chloroplasts isolated from greening cotyledons contained endogenous amounts of protoporphyrin, of magnesium-protoporphyrin monoester, and longer wavelength metalloporphyrins, and these tetrapyrroles were presumed to be intermediates of the protochlorophyll biosynthetic pathway
Summary
Developing chloroplasts were isolated from greening Cucumis cotyledons in a cofactor-enriched medium and were incubated in the dark with W-labeled and unlabeled magnesium-protoporphyrin monoester. The metabolic pools between protoporphyrin and protochlorophyllide were monitored spectrofluorometrically. It was shown that magnesium-protoporphyrin monoester, a postulated intermediate of the chlorophyll biosynthetic pathway, was convertible into protochlorophyllide with relatively high yields. Since protochlorophyllide is the immediate precursor of chlorophyll a it was concluded that magnesiumprotoporphyrin monoester was an intermediate of the chlorophyll biosynthetic pathway. IX and magnesiumprotoporphyrin monoester are intermediates of the chlorophyll biosynthetic pathway (5). This assumption has never been directly verified by demonstrating, for example, the conversion of protoporphyrin. With the recent development of cell-free systems capable of protochlorophyll and chlorophyll biosynthesis from &aminolevulinic acid (6-9) and the development of sensitive spectrofluorometric protoporphyrin techniques to monitor
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